This invention relates to the field of printed, optically-encoded data and to techniques for reading it.
Prior optical systems have primarily utilized bar codes or codes utilizing character recognition, such as check-identification codes. Neither have permitted high density concentrations of information.
Bar codes utilize bars of varying widths, the widths usually bearing a ratio relationship to each other (such as 1:2:3); and the heights of the bars are not critical but must be adequately long to accommodate the scanner. The speed of scanning need not be pre-determined, since it is deduced by the reader during scanning, nor must the speed be constant during scanning. This imposes minimum practical widths and heights on the bars, and so limits the density of encoded information.
Optical character recognition requires characters of a minimum size and requires the utilization of multiple scans of each line in order to identify the character.
By contrast, the present invention utilizes a high-density data strip formed of a plurality of narrow "data lines" formed of uniform size, generally rectangular "bit areas". These bit areas are on paper or other substrate and are either dark (printed) or blank. The data lines are of uniform width and length, parallel, contiguous, and conterminous. Their combined widths form the longitudinal dimension of the encoded information portion of the data strip; and the bit areas are aligned in this longitudinal direction. The density concentration of bit areas is such that a typical strip might include 62 bit areas per data line and 300 data lines, thus providing 7,200 bits of information in a strip measuring, perhaps, 12.5.times.90 mm (0.5.times.3.5 inches).
The method and scanner of the present invention can not only be used to read strips of high-density data, but also to read strips having different densities. These different densities result from using different widths and heights of data areas. The data lines forming the data strip may vary in length or number from strip to strip.
The invention has means to self-adjust alignment of the strip with the scanner, both prior to and during scanning, and can also self-adjust its scanning rate for changes in density. It can utilize different inks, papers and substrates, and adjust for the relative contrasts between them. Its parity system can correct errors occurring in scanner readings due, for example, to scratches or the presence of dirt on some of the data areas.
Examples of bar and other codes and reading methods are found in Wilson U.S. Pat. No. 3,211,470, Seligman U.S. Pat. No. 4,049,224, and Bullis U.S. Pat. No. 4,308,455. Additional patents showing systems for reading are Sharkitt U.S. Pat. No. 3,780,271, Dolch U.S. Pat. No. 3,852,573, Lloyd U.S. Pat. No. 3,886,371, Laurer, U.S. Pat. No. 4,414,468; and certain types of apparatus are shown in Freidman U.S. Pat. No. 3,716,660 and Ortman U.S. Pat. No. 3,549,894.